The present invention relates to an electromagnet for controlling the metering valve of a fuel injector, comprising a fixed core of magnetizable material, an electric energizing coil, and an armature for activating the valve.
The metering valves of fuel injectors normally comprise a control chamber having a drain conduit which, by means of a shutter, is normally closed by the armature of the electromagnet, and is opened by energizing the electromagnet and so moving the armature towards the core.
As is known, the main parameter for evaluating the efficiency of a metering valve is the maximum permissible operating frequency, which depends on the speed with which the valve responds to a command to open or close the drain conduit, and hence on the speed with which it responds to energizing or de-energizing of the electromagnet.
In known metering valves, the fixed core of the electromagnet is made of magnetizable ferrous material, usually ferrite, which, despite good magnetic permeability, presents a considerable hysteresis loop, and is subject to severe parasitic currents, which seriously impair the magnetic force of the core.
Known cores therefore take a relatively long time to reach the necessary magnetic force, thus limiting both the response of the electromagnet and maximum operating frequency. As a result, to speed up response, the core and coil must be oversized, thus greatly increasing both production and operating cost.